Communication Control Apparatus and Communication Terminal

ABSTRACT

A communication control apparatus for controlling communication by repeatedly sending a control signal to other apparatuses at a given time interval, the communication using a protocol that regulates transmissions of an acknowledgement as a receipt for one or more communication packets, and the control signal allocating, within the given time interval, two types of communication periods which are (i) a one-way communication period in which a one-way communication is performed and (ii) a two-way communication period in which a two-way communication is performed. The communication control apparatus determines, based on an occurrence ratio of the transmissions of the acknowledgement, a length of the one-way communication period, and sends the control signal that allocates a plurality of the one-way communication periods each of which has the determined length.

TECHNICAL FIELD

The present invention relates to a communication control apparatus thatcontrols communication performed by each communication terminal byperiodically transmitting a control signal thereto. Particularly, thepresent invention relates to a method for allocating bandwidth forcontrolling Quality of Service (QoS), in a case where communication isperformed using a protocol, such as a transmission control protocol(TCP).

BACKGROUND ART

The IEEE 802. 11e standard formulates a technology for achieving QoScontrol in a wireless communication system, which is comprised of (i) acommunication control apparatus that periodically transmits a controlsignal and (ii) a communication terminal that performs wirelesscommunication in accordance with the control signal transmitted by thecommunication control apparatus (see Non-Patent Reference 1). Two accesscontrol methods are standardized in the IEEE 802. 11e: an enhanceddistributed channel access (EDCA); and a hybrid coordination functioncontrolled channel access (HCCA).

EDCA achieves the QoS control by giving high priority data a good chanceof being transmitted. With the EDCA, each of the communication terminalsobtains channel access with high probability. In contrast, HCCA achievesthe QoS control by allocating a given bandwidth to a specificcommunication terminal. With the HCCA, a direction of data transmissionsis limited to either one of “down-link” (from the communication controlapparatus to the communication terminal) or “up-link” (from thecommunication terminal to the communication control apparatus). Byentitling only one specific communication terminal to the channelaccess, the HCCA can guarantee allocation of the bandwidth to thespecific communication terminal.

The communication control apparatus allocates two types of communicationperiods within a time interval between control signal transmissions,depending on requested bandwidth for transmitting data. One is an HCCAperiod in which communication is performed with the HCCA, and the otheris an EDCA period in which the communication is performed with the EDCA.The communication control apparatus then transmits the control signal,including information indicative of the above allocations. Each of thecommunication terminals performs the communication in accordance withthe above allocations of the HCCA and EDCA that is indicated by thecontrol signal. In this structure, data that requires an adequate amountof bandwidth can be transmitted with the HCCA, so that the datatransmission is not affected by other data transmissions. Meantime, datathat does not require such a bandwidth can be transmitted with the EDCA.

Non-Patent Reference 1:

IEEE P802.11e/D11.0, “IEEE Standard for InformationTechnology—Telecommunications and information exchange betweensystems—Local and metropolitan area networks Specific requirements—Part11: Wireless Medium Access Control (MAC) and Physical Layer (PHY)specifications: Amendment 7: Medium Access Control (MAC) Quality ofService (QoS) Enhancements”, October 2004

DISCLOSURE OF THE INVENTION The Problems the Invention is Going to Solve

As mentioned above, only a one-way communication can be performed in theHCCA period. In this light, the QoS control can be achieved in the HCCAperiod, if the communication is performed with use of a user datagramprotocol (UDP), including a real-time transport protocol (RTP), thatdoes not require an acknowledgment of whether the data has beenreceived.

However, if the communication is performed with use of a protocol (e.g.,TCP) that regulates data transmissions while transmitting/receiving theacknowledgement as a receipt for the data, a data transmitting apparatuscannot continue the data transmissions until it has received an ACKsignal, which is the acknowledgement as a receipt for the data. On theother hand, in the HCCA period that only permits the one-waycommunication, a data receiving apparatus cannot transmit the ACK signalcorresponding to the received data. As a result, when the communicationis performed using protocols such as TCP, the following problem arises:despite the fact that the communication control apparatus has allocatedthe HCCA period to guarantee the bandwidth, the data is transmitted inan unstable condition due to an absence of the transmissions/receptionsof the ACK signal.

In view of the above problem, it is an object of the present inventionto provide a communication control apparatus and a communicationterminal that can stably transmit data that requires an adequate amountof bandwidth, even in the case of using a protocol that regulates thedata transmissions while transmitting/receiving the acknowledgement asthe receipt for the data.

Means to Solve the Problems

To solve the above problem, the present invention provides acommunication control apparatus for controlling communication byrepeatedly sending a control signal to other apparatuses at a given timeinterval, the communication using a protocol that regulatestransmissions of an acknowledgement as a receipt for one or morecommunication packets, and the control signal allocating, within thegiven time interval, two types of communication periods which are (i) aone-way communication period in which a one-way communication isperformed and (ii) a two-way communication period in which a two-waycommunication is performed, the communication control apparatuscomprising: a storing unit in which an occurrence ratio of thetransmissions of the acknowledgement is stored; a determination unitoperable to determine, based on the stored occurrence ratio of thetransmissions of the acknowledgement, a length of the one-waycommunication period; and a communication control unit operable togenerate and send the control signal that allocates a plurality of theone-way communication periods each of which has the determined length.

EFFECTS OF THE INVENTION

With the above structure, the communication control apparatus determinesthe length of the one-way communication period based on the occurrenceratio of the transmissions of the acknowledgement. The communicationcontrol apparatus can thereby allocate each of the communication periodswithin the given time interval so as to (i) send the one or morecommunication packets in the one-way communication period, and (ii) setthe two-way communication period in which the acknowledgement, which isthe receipt for the one or more communication packets, is transmitted.

Compared to a case where each of the communication periods is allocatedonly based on the bandwidth that is requested for transmitting the data,the above structure can reduce a situation where the communicationpackets cannot be transmitted successively because the acknowledgementis not transmitted/received in the one-way communication period. Theabove structure thus enables efficient and stable data transmissions.

The determination unit may determine, based on the stored occurrenceratio of the transmissions of the acknowledgement, the length of each ofthe one-way communication periods to be a time needed for thecommunication control apparatus to transmit data as the one or morecommunication packets, a size of the data corresponding to apredetermined number of the acknowledgements.

With the above structure, the communication control apparatus canallocate each of the communication periods such that the two-waycommunication period, in which the acknowledgement is transmitted,follows immediately after each of the one-way communication periods, inwhich the one or more communication packets, whose data size correspondsto a given number of the acknowledgements, are transmitted. This way atime frame in which the one or more communication packets cannot betransmitted due to an absence of the acknowledgementtransmissions/receptions can be set within a shortest period possible.Accordingly, the communication control apparatus can transmit dataefficiently and stably.

The data receiving apparatus stores the occurrence ratio of thetransmissions of the acknowledgment. In contrast, there is a case wherethe data transmission apparatus does not have this occurrence ratio ofthe transmissions of the acknowledgement stored therein.

In view of this, the communication control apparatus may further includea measuring unit operable to, if transmitting the communication packetsto one of the other apparatuses, measure the occurrence ratio of thetransmissions of the acknowledgement based on a number of the receivedacknowledgements from the one of the other apparatuses, each of thereceived acknowledgements corresponding to a size of data that istransmitted as the one or more communication packets, wherein themeasured occurrence ratio of the transmissions of the acknowledgement isstored in the storing unit.

The above structure allows the communication control apparatus to, iftransmitting the communication packets to one of the other apparatuses,measure the occurrence ratio of the transmissions of the acknowledgementsolely on its own. Therefore, even if the communication controlapparatus has not stored therein the occurrence ratio of thetransmissions of the acknowledgment, the communication control apparatuscan transmit the data efficiently by measuring the occurrence ratio ofthe transmissions of the acknowledgement.

The communication control apparatus may further include an acquisitionunit operable to, if transmitting the one or more communication packetsto one of the other apparatuses, acquire the occurrence ratio of thetransmissions of the acknowledgement from the one of the otherapparatuses, wherein the acquired occurrence ratio of the transmissionsof the acknowledgement is stored in the storing unit.

To solve the stated problem, the present invention may also provide acommunication terminal for performing communication using a protocolthat regulates transmissions of an acknowledgement as a receipt for oneor more communication packets in accordance with the control signal sentby the above communication control, apparatus, the communicationterminal comprising: a communication unit operable to transmit andreceive the one or more communication packets, and a notifying unitoperable to, if receiving the communication packets from thecommunication control apparatus, notify the communication controlapparatus of an occurrence ratio of the transmissions of theacknowledgement.

With this structure, the communication control apparatus, which controlsthe communication performed by the communication terminal, can obtainthe occurrence-ratio of the transmissions of the acknowledgement fromthe communication terminal if transmitting the communication packets.Accordingly, the communication control apparatus can transmit dataefficiently.

To solve the stated problem, the present invention may further provide acommunication control method for controlling communication by repeatedlysending a control signal to other apparatuses at a given time interval,the communication using a protocol that regulates transmissions of anacknowledgement as a receipt for one or more communication packets, andthe control signal allocating, within the given time interval, two typesof communication periods which are (i) a one-way communication period inwhich a one-way communication is performed and (ii) a two-waycommunication period in which a two-way communication is performed, thecommunication control apparatus comprising: a storing step of storing anoccurrence ratio of the transmissions of the acknowledgement; adetermination step of determining, based on the stored occurrence ratioof the transmissions of the acknowledgement, a length of the one-waycommunication periods and a communication control step of generating andsending the control signal that allocates a plurality of the one-waycommunication periods each of which has the determined length.

To solve the stated problem, the present invention may provide acommunication method of a communication terminal for performingcommunication using a protocol that regulates transmissions of anacknowledgement as a receipt for one or more communication packets, thecommunication being performed in accordance with the control signal sentby the communication control apparatus, the communication methodcomprising: a communication step of transmitting and receiving the oneor more communication packets, and a notifying step of, if receiving theone or more communication packets from the communication controlapparatus, notifying the communication control apparatus of anoccurrence ratio of the transmissions of the acknowledgement.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a communication system of the present invention.

FIG. 2 is a functional block diagram illustrating structures of acommunication control apparatus 100 and communication terminals 500 thatconstitute the communication system of the present invention.

FIGS. 3A and 3B show diagrams pertaining to an ACK delay value.

FIG. 4 is a flowchart illustrating a process in which the communicationcontrol apparatus 100 generates a control signal based on the ACK delayvalue and sends the control signal.

FIG. 5 shows a diagram indicating allocations of HCCA and EDCA periodswithin a time interval between control signal transmissions.

DESCRIPTION OF CHARACTERS

-   1 Network-   2 Data Server-   11 Antenna-   12 Transmitting/Receiving Unit-   13 Protocol Processing Unit-   14 ACK Delay Value Management Unit-   15 Bandwidth Setting Unit-   16 Communication Control Unit-   51 Antenna-   52 Transmitting/Receiving Unit-   53 Protocol Processing Unit-   54 ACK Delay Value Setting Unit-   55 Data Processing Unit-   100 Communication Control Apparatus-   500 Communication Terminals

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment

The following describes an embodiment of a communication system of thepresent invention with use of the drawings, the communication systemincluding a communication control apparatus and a communicationterminal.

Overview

FIG. 1 shows a communication system of the present invention.

The communication system of the present invention includes: a dataserver 2, a communication control apparatus 100, a plurality ofcommunication terminals 500 (communication terminals 500 a, 500 b, 500 c. . . ). The data server 2 and the communication control apparatus 100are connected to an outside network 1. Each of the communicationterminals 500 is connected to the network 1 via the communicationcontrol apparatus 100.

The data server 2 has stored therein audio-visual data and the like thathave been acquired from outside sources, including the outside network1.

The communication control apparatus 100, which is connected to thenetwork 1, communicates with the data server 2 and each of thecommunication terminals 500. The communication apparatus 100 also sendsa control signal to each of the communication terminals 500 periodicallyto control communication performed by each of the communicationterminals 500.

The communication terminals 500 receive the control signal sent by thecommunication apparatus 100, and perform the communication according tothe received control signal.

Note that in the present embodiment, the communication control apparatus100 and each of the communication terminals 500 communicate with oneanother wirelessly, achieving the QoS control in line with the IEEE 802.11e standard. The communication control apparatus 100 allocates twotypes of periods within the time interval between the control signaltransmissions: an HCCA period in which communication is performed withthe HCCA; and an EDCA period in which the communication is performedwith the EDCA. The communication control apparatus 100 then transmitsthe control signal indicative of the above allocations. Thecommunication terminals 500, which receive the control signalperiodically, perform the wireless communication in accordance with theabove allocations of the HCCA and EDCA indicated by the received controlsignal.

The present invention can be applied to the above communication systemif the communication is performed with use of a protocol that regulatestransmissions of an acknowledgement as a receipt for one or morecommunication packets. In the following description of the presentinvention, TCP is used as an example of the protocol that regulatestransmissions of the acknowledgement.

More specifically, the communication system of the present inventionpartially makes up a home network and the like. In this home network,the communication terminals 500 request that the audio-visual data andthe like, which has been stored in the data server 2, be transmittedthereto. The communication terminals 500 receive the data they requestedvia the communication control apparatus 100. Here, the communicationterminals 500 transmit an ACK signal each time they receive a given sizeof data as packets. This transmission is based on an ACK delay valuethat indicates how much data in size (how many packets) thecommunication terminals 500 should receive before transmitting the ACKsignal, namely the acknowledgement. For example, if the ACK delay valueis “4,” it means the communication terminals 500 transmit the ACK signaleach time they receive four packets' worth of data; the communicationterminals 500 thereby transmit the ACK signal each time they receivefour packets.

The communication control apparatus 100 has the ACK delay value storedtherein. Based on (i) bandwidth needed to transmit data requested by theterminals 500 and (ii) the ACK delay value, the communication controlapparatus 100 allocates the HCCA period within the time interval toguarantee the above bandwidth.

<Structure>

Described below are structures of the communication control apparatus100 and the communication terminals 500 of the present invention.

FIG. 2 is a functional block diagram illustrating structures of thecommunication control apparatus 100 and the communication terminals 500that constitute the communication system of the present invention.

As illustrated in FIG. 2, the communication control apparatus 100includes: an antenna 11; a transmitting/receiving unit 12; a protocolprocessing unit 13; an ACK delay value management unit 14; a bandwidthsetting unit 15; and a communication control unit 16. The communicationcontrol apparatus 100 is connected to the data server 2.

The antenna 11 sends and receives a wireless signal.

The transmitting/receiving unit 12 modulates data to be transmitted intoa wireless signal, and sends the wireless signal via the antenna 11. Thetransmitting/receiving unit 12 also demodulates a wireless signalreceived via the antenna 11 into data, and outputs the data to theprotocol processing unit 13.

As controlled by the communication control unit 16, the protocolprocessing unit 13 receives data to be transmitted (e.g., data that thedata server 2 is going to transmit to other apparatus). The protocolprocessing unit 13 then adds a given protocol header (e.g., aTCP-header) to the data, and outputs the data to thetransmitting/receiving unit 12. The protocol processing unit 13 alsoreceives data from the transmitting/receiving unit 12. Here, in order toobtain the data, the protocol processing unit 13 performs tasks such asanalyzing a header of the data. After obtaining the data, the protocolprocessing unit 13 outputs the data to the ACK delay value managementunit 14 and the like.

The ACK delay value management unit 14 stores and manages the ACK delayvalue of the communication terminals 500, and outputs the ACK delayvalue to the communication control unit 16.

The bandwidth setting unit 15 manages bandwidth that is requested fortransmitting data, and outputs the requested bandwidth to thecommunication control unit 16. The bandwidth setting unit 15 alsoreceives from other apparatuses (e.g., the data server 2) informationregarding the bandwidth requested for transmitting the data.

The communication control unit 16 controls communication performedbetween the communication control apparatus 100 and other apparatuses.Based on (i) the ACK delay value received from the ACK delay valuemanagement unit 14 and (ii) the requested bandwidth that is input fromthe bandwidth setting unit 15, the communication control unit 16allocates two types of communication periods, namely the HCCA period andthe EDCA period, within the time interval. The communication controlunit 16 then performs processings (e.g., controlling the protocolprocessing unit 13) so as to send the control signal indicative of theallocations.

As illustrated in FIG. 2, each of the communication terminals 500includes: an antenna 51; a transmitting/receiving unit 52; a protocolprocessing unit 53; an ACK delay value setting unit 54; and a dataprocessing unit 55.

The antenna 51 sends and receives a wireless signal.

The transmitting/receiving unit 52 modulates data to be transmitted intoa wireless signal, and transmits the wireless signal via the antenna 51.The transmitting/receiving unit 52 also demodulates a wireless signalreceived via the antenna 11 into data, and outputs the data to theprotocol processing unit 53.

As controlled by the data processing unit 55, the protocol processingunit 53 adds a given protocol header (e.g., the TCP header) to data tobe transmitted, and then outputs the data to the transmitting/receivingunit 52. The protocol processing unit 53 also receives data from thetransmitting/receiving unit 52. Here, in order to obtain the data, theprotocol processing unit 53 performs tasks such as analyzing a header ofthe data. After obtaining the data, the protocol processing unit 53outputs the data to the data processing unit 55.

The ACK delay value setting unit 54 has the ACK delay value storedtherein.

The data processing unit 55 controls data-related processings,including: transmitting the ACK signal; transmitting the ACK delay valueto the communication control apparatus 100 by controlling the protocolprocessing unit 53; and outputting data that the communication terminals500 have received to an outside display device.

Specifically, the communication control apparatus 100 and thecommunication terminals 500 described above are equipped with a centralprocessing unit (CPU), a read only memory (ROM), a random access memory(RAM), a modulation/demodulation circuit, and so on. The communicationcontrol apparatus 100 and the communication terminals 500 operate inaccordance with a program stored in the ROM.

<Data>

The following describes main data and data structure that are used inthe present embodiment.

FIGS. 3A and 3B show diagrams pertaining to the ACK delay value.

In the present embodiment, it is assumed that the ACK delay value is thenumber of packets the communication terminals 500 receive beforetransmitting one ACK signal. FIG. 3A shows the ACK delay value being “4”as an example. Here, the communication terminals 500 transmit the ACKsignal each time they receive four packets that are transmitted inaccordance with TCP.

In the present embodiment, as shown in FIG. 3B, the communicationterminals 500 inform the communication control apparatus 100 of the ACKdelay value by transmitting data to the control apparatus 100, the dataincluding the ACK delay value. FIG. 3B gives an example of the ACK delayvalue being informed to the communication control apparatus 100 togetherwith each transmission of the ACK signal.

<Operation>

The communication control apparatus 100 of the present inventionallocates, based on the ACK delay value, two types of communicationperiods within the time interval: the HCCA period and the EDCA period.Once the communication control apparatus 100 and the communicationterminals 500 establish communication using TCP, the communicationterminals 500 transmit a packet that includes the ACK signal to thecommunication control apparatus 100 (the packets correspond to data thatthe communication terminals 500 have received from the communicationcontrol apparatus 100). Here, the communication terminals 500 add theACK delay value into the above packet so as to inform the communicationcontrol apparatus 100 of the ACK delay value. It is considered that thecommunication terminals 500 receive data that has required and has beenprovided with a given bandwidth, where as the communication controlapparatus 100 uses the HCCA to transfer data that has required and hasbeen provided with a given bandwidth.

FIG. 4 is a flowchart illustrating a process in which the communicationcontrol apparatus 100 generates the control signal based on the ACKdelay value and sends the control signal.

After starting the communication with the communication terminals 500,the communication control apparatus 100 receives the packet thatincludes the ACK signal and the ACK delay signal from the communicationterminals 500. The protocol processing unit 13 obtains the ACK delayvalue included in the received packet by analyzing the packet, and thenoutputs the obtained ACK delay value to the ACK delay value managementunit 14. The ACK delay value management unit 14 stores the ACK delayvalue therein (step S41).

Once the ACK delay value management unit 14 stores the ACK delay valuetherein, the communication control unit 16 receives (i) from thebandwidth setting unit 15 information regarding bandwidth that isrequested for transferring data, and (ii) from the ACK delay valuemanagement unit 14 the ACK delay value. Based on the received ACK delayvalue, the communication control unit 16 calculates a length of one HCCAperiod (step S42).

FIG. 5 shows the allocations of the HCCA period and the EDCA periodwithin the time interval. In FIG. 5, it is specifically provided that P(bps) is a maximum transfer rate indicating a maximum amount of datathat can be transmitted through a channel; q (seconds) is a length ofthe time interval between the control signal transmissions; r (bps) isbandwidth that is requested for transferring data; s (bits) is a size ofdata per packet; and t is the ACK delay value. In this regard, thelength of one HCCA period can be calculated by the following formula:st/P. That is, the length of one HCCA period is a time needed totransmit the number of packets indicated by the ACK delay value.

After calculating the length of one HCCA period, the communicationcontrol unit 16 calculates the number of the HCCA periods within thetime interval between the control signal transmissions based on thebandwidth requested for transferring the data and the ACK delay value(step S43).

As shown in FIG. 5, n (the number of the HCCA period within the timeinterval between the control signal transmissions) can be calculated bythe following formula: n=rq/(st). In other words, the number of the HCCAperiods can be obtained by dividing (i) rq (bits), which is a size ofdata to be transferred using HCCA in the time interval between thecontrol signal transmissions, by (ii) st (bits), which is a size of datato be transmitted in one HCCA period.

Following the calculation of n (the number of the HCCA periods withinthe time interval between the control signal transmissions), thecommunication control unit 16 generates a control signal that instructsto allocate the EDCA period following each of the HCCA periods.Specifically, each of the HCCA periods and the EDCA periods is allocatedso that there are a total of n pairs of the HCCA period and the EDCAperiod. As there are n pairs of the HCCA period and the EDCA period intotal, a length of one pair thereof would be obtained by the followingformula: q/n. The communication control apparatus 100 sends thegenerated control signal (step S44).

Modification Examples

Use of TCP for transmitting data generally leads to the followingsituations. Immediately after the start of the transmission, anoccurrence ratio of the transmissions of the ACK signal, which is areceipt for one or more communication packets, is high. However, thelonger the communication time becomes, the less frequently the ACKsignal is transmitted/received. That is to say, the ACK delay value issmall right after the start of the transmission, but over time, the ACKdelay value will gradually become larger. In the case where the data istransmitted in a stable condition, the data transmission will becomemore efficient by decreasing the occurrence ratio of thetransmissions/receptions of the ACK signal.

For example, immediately after the start of the transmission, the ACKsignal is transmitted/received each time one packet is transmitted. Inthe meantime, the ACK signal will eventually be transmitted/receivedeach time a plurality of packets are transmitted.

Also, if the data transmission yields no packet loss for a given timeperiod, the ACK delay value will become and remain at a fixed value.

In this regard, the communication control apparatus 100 may executeprocessings (e.g., the above steps S42 and S43) based on an occurrencerate of packet communication error, after the occurrence rate of packetcommunication error falls to or below a predetermined rate (for example,after the rate becomes 1% or below). This can prevent the allocations ofeach of the HCCA periods within the time interval while the ACK delayvalue is undergoing a change.

It should be noted that if a transmission error occurs due to packetloss and other reasons, the occurrence ratio of thetransmissions/receptions of the ACK signal will increase, just like itdoes immediately after the data transmission starts. In this case, thecommunication control apparatus 100 may also execute the processings(e.g., the above step S42) after the error occurrence rate falls to orbelow the predetermined rate.

The foregoing has described the case where the communication controlapparatus 100 executes the processings based on the occurrence rate ofpacket communication error. Other than this case, the communicationcontrol apparatus 100 may wait to execute the processings (e.g., theabove step S42) until a given time period has passed since the start ofthe communication. An example of the above given time period is the timeuntil a start of the stable data transmission, which occurs after thepacket loss rate drops to or below a predetermined rate. Or, the abovegiven time period may be the time until the start of the stable datatransmission, the time that has been measured in advance. In a casewhere the communication control apparatus 100 obtains the ACK delayvalue from the communication terminals 500, the communication terminals500 may not transmit the ACK delay value until the above given time haspassed.

<Additional Information>

Although the communication control apparatus and communicationterminals, which constitute the communication system of the presentinformation, have been described above based on the embodiment, they mayinstead operate as described in the following modification examples. Thecommunication control apparatus and communication terminals described inthe above embodiment are not intended to limit the present invention.

(1) The above embodiment has exemplarily described the communicationcontrol apparatus and the communication terminals that achieve, in linewith the IEEE 802. 11e standard, the QoS control with use of HCCA andEDCA. However, regardless of the IEEE 802. 11e standard, the presentinvention can be realized in a communication system in which the one-waycommunication period and the two-way communication period coexist.

Although the above embodiment has used TCP as an, example of theprotocol that regulates the transmissions/receptions of theacknowledgement, other protocols may be used instead of TCP.

Under the assumption that the ACK signal is transmitted/received duringthe EDCA period, the EDCA period follows after the HCCA period in theabove embodiment. However, it is not required that the ACK signaltransmissions/receptions be performed during the EDCA period. Instead ofthe EDCA period, the HCCA period may be allocated such that the ACKsignal is transmitted over the up-link channel from the communicationterminals 500 to the communication apparatus 100.

(2) According to the above embodiment, the communication terminals 500inform the communication apparatus 100 of the ACK value by including theACK delay value into the packet that is to be transmitted for deliveringthe ACK signal. However, the communication control apparatus 100 mayobtain the ACK delay value in other ways. For example, the communicationterminals 500 may use alternative methods for informing thecommunication control apparatus 100 of the ACK delay value. Or, thecommunication control 100 may give a certain instruction to thecommunication terminals 500 to obtain the ACK delay value therefrom. Itshould be noted here that the present invention includes thecommunication terminals 500 that receive the above instruction andtransmit the ACK delay value to the communication control apparatus 100.

The communication control apparatus 100 may also measure (i) the numberof packets transmitted to the communication terminals 500, (ii) the sizeof data that is transmitted as packets, and (iii) the number of the ACKsignals received from the communication terminals 500, so as tocalculate and store the ACK value based on the measurement.

According to the above embodiment, the ACK delay value is expressedbased on the number of packets that have been transmitted to thecommunication terminals. Instead, the ACK delay value may be expressedbased on other criteria, such as the size of data that has beentransmitted as packets.

(3) In the above embodiment, the length of the HCCA period is explainedas the time needed to transmit the number of packets corresponding toone ACK signal, transmission. The length of the HCCA period, however,may be calculated in other methods. For example, the length of the HCCAperiod may be the time needed to transmit the number of packetscorresponding to a plurality of ACK signal transmissions. Or, the lengthof the HCCA period may be a preset certain time period. A plurality ofthe HCCA periods and a plurality of the EDCA periods included in thetime interval between the control signal transmissions may havedifferent length from one another.

(4) Specifically, each apparatus described above is a computer systemcomprised of a microprocessor, ROM, RAM, a hard disc unit, a displayunit, a keyboard, a mouse, and so on. The RAM or the hard disc containsa computer program stored therein. The devices achieve their functionswith the microprocessor operating in accordance with the computerprogram. Here, the computer program is comprised of a plurality ofopcodes that are instructions given to a computer. With thisconstruction the computer program can achieve its certain function.

(5) Part of, or all of components of each apparatus may be comprised ofone system LSI (large scale integration). The system LSI is asuper-multifunction LSI, specifically a computer system comprised of themicroprocessor, ROM, RAM, and so on. The system LSI is manufactured insuch a way that a plurality of components are integrated on one chip.The RAM contains the computer program stored therein. The system LSIachieves its function with the microprocessor operating in accordancewith the computer program.

(6) Part of, or all of components of each apparatus may be comprised of(i) an IC card that is attachable to and removable from each apparatus,or (ii) a single module. The IC card and the module are each a computersystem comprised of the microprocessor, ROM, RAM, and so on, and mayinclude the system LSI described above. The IC card or the moduleachieves its function with the microprocessor operating in accordancewith the computer program. The IC card or the module may betamper-resistant.

(7) The present invention may be methods that are described above. Theypresent invention may also be a computer program that realizes suchmethods with use of a computer, or be a digital signal comprised of thecomputer program.

Furthermore, the present invention may be a computer-readable recordingmedium storing the computer program or the digital signal. The computerreadable recording medium includes a flexible disc, a hard disc, aCD-ROM, an MO, a DVD, a DVD-ROM, a DVD-RAM, a BD (Blu-ray Disc), asemiconductor memory, and so on. Or, the present invention may be thecomputer program or the digital signal being recorded onto/into theabove computer-readable recording medium.

The present invention may be the computer program or the digital signalthat are transmitted via an electric communication network, a wirelessor wired communication network, a network (typically the Internet), adata broadcast, and so on.

Furthermore, the present invention may be a computer system including amicroprocessor and a memory, the memory storing the computer programtherein. The microprocessor may operate in accordance with the computerprogram.

Furthermore, the present invention may be executed by anotherindependent computer system, by having the computer program or thedigital signal stored onto/into the above recording medium andtransferred, or by having the computer program or the digital signaltransferred via the network.

(8) The present invention may be any combination of the embodiment andmodification examples described above.

INDUSTRIAL APPLICABILITY

In a communication network in which audio-visual data such as MPEG2-TSis transmitted, the communication control apparatus and thecommunication terminals of the present invention can be used forachieving the QoS control using a protocol (e.g., TCP) that regulatesthe transmissions/receptions of the acknowledgement. The communicationcontrol apparatus and the communication terminals are advantageous whenused for distributing videos and for other purposes.

1. A communication control apparatus for controlling communication byrepeatedly sending a control signal to other apparatuses at a given timeinterval, the communication using a protocol that regulatestransmissions of an acknowledgement as a receipt for one or morecommunication packets, and the control signal allocating, within thegiven time interval, two types of communication periods which are (i) aone-way communication period in which a one-way communication isperformed and (ii) a two-way communication period in which a two-waycommunication is performed, the communication control apparatuscomprising: a storing unit in which an occurrence ratio of thetransmissions of the acknowledgement is stored; a determination unitoperable to determine, based on the stored occurrence ratio of thetransmissions of the acknowledgement, a length of the one-waycommunication period; and a communication control unit operable togenerate and send the control signal that allocates a plurality of theone-way communication periods each of which has the determined length.2. The communication control apparatus of claim 1, wherein thedetermination unit determines, based on the stored occurrence ratio ofthe transmissions of the acknowledgement, the length of each of theone-way communication periods to be a time needed for the communicationcontrol apparatus to transmit data as the one or more communicationpackets, a size of the data corresponding to a predetermined number ofthe acknowledgements.
 3. The communication control apparatus of claim 1,further comprising: a measuring unit operable to, if transmitting theone or more communication packets to one of the other apparatuses,measure the occurrence ratio of the transmissions of the acknowledgementbased on a number of the received acknowledgements from the one of theother apparatuses, each of the received acknowledgements correspondingto a size of data that is transmitted as the one or more communicationpackets, wherein the measured occurrence ratio of the transmissions ofthe acknowledgement is stored in the storing unit.
 4. The communicationcontrol apparatus of claim 1, further comprising: an acquisition unitoperable to, if transmitting the one or more communication packets toone of the other apparatuses, acquire the occurrence ratio of thetransmissions of the acknowledgement from the one of the otherapparatuses, wherein the acquired occurrence ratio of the transmissionsof the acknowledgement is stored in the storing unit.
 5. A communicationterminal for performing communication using a protocol that regulatestransmissions of an acknowledgement as a receipt for one or morecommunication packets in accordance with the control signal sent by thecommunication control apparatus of claim 4, the communication terminalcomprising: a communication unit operable to transmit and receive theone or more communication packets, and a notifying unit operable to, ifreceiving the one or more communication packets from the communicationcontrol apparatus, notify the communication control apparatus of anoccurrence ratio of the transmissions of the acknowledgement.
 6. Acommunication control method for controlling communication by repeatedlysending a control signal to other apparatuses at a given time interval,the communication using a protocol that regulates transmissions of anacknowledgement as a receipt for one or more communication packets, andthe control signal allocating, within the given time interval, two typesof communication periods which are (i) a one-way communication period inwhich a one-way communication is performed and (ii) a two-waycommunication period in which a two-way communication is performed, thecommunication control apparatus comprising: a storing step of storing anoccurrence ratio of the transmissions of the acknowledgement; adetermination step of determining; based on the stored occurrence ratioof the transmissions of the acknowledgement, a length of the one-waycommunication period; and a communication control step of generating andsending the control signal that allocates a plurality of the one-waycommunication periods each of which has the determined length.
 7. Acommunication method of a communication terminal for performingcommunication using a protocol that regulates transmissions of anacknowledgement as a receipt for one or more communication packets, thecommunication being performed in accordance with the control signal sentby the communication control apparatus of claim 4, the communicationmethod comprising: a communication step of transmitting and receivingthe one or more communication packets, and a notifying step of, ifreceiving the one or more communication packets from the communicationcontrol apparatus, notifying the communication control apparatus of anoccurrence ratio of the transmissions of the acknowledgement.